Various techniques and equipment have been developed to ensure efficient and clean operation of burners used in power generation, industrial, commercial, and residential furnaces, heat treating ovens, and boilers. These techniques include the use of sampling probes that are inserted into a flue or other pipe or duct and configured to extract a sample of flowing gas for analysis, such as for measurement of carbon monoxide levels.
In applications where the gas stream contains particulate matter, the gas is typically filtered at the sampling point, to prevent the particles from reaching the analysis point. Various filters, including sintered metal filters, have been used for this purpose. However, it is well known that these filters can become clogged and must be periodically cleaned, preferably without removing the probe from service. To address this problem, various methods for purging the filters have been developed. In many cases, a sampling tube, which normally carries a sample of the gas to an analysis unit, is pressurized, to force air through the probe in a reverse direction, thus cleaning the filter. One problem with this approach is that moisture in the sampling line is forced through the filter and probe head. This moisture can combine with the gas particles to clog the filter and/or other parts of the probe. Accordingly, improved techniques and devices for extracting gas samples from a particle-laden fluid stream are needed.